The NAHL houses three facilities: (1) Actively Controlled Expansion Tunnel (ACE), (2) Mach 6 Quiet Tunnel (M6QT), and (3) Hypervelocity Expansion Tunnel (HXT). The researchers within the NAHL also have access to the test facilities associated with the Bush Combat Development Center (BCDC).
HXT utilizes a 0.5-m diameter shock tube fitted with a 3-ft exit diameter nozzle and is tailored to provide true temperature “aerothermally clean” air for Mach numbers up to 15 (12 MJ/kg). Beyond this, the flow experiences real gas effects in the freestream. The facility can produce flight enthalpy test conditions to Mach 25. However, the facility can also be operated in a cold flow mode for high Reynolds numbers. The low Reynolds number operation is enabled by the use of an additional turbo pump to reduce the pressure within the accelerator section to 10-4 Torr.
The ACE tunnel and M6QT share an air supply and vacuum system. The high-pressure air is filtered (99% efficient sub-micron), desiccant dried to 233K, and stored in a 23.5 m3 tank at 170 atm. Air to the tunnels is heated by a 0.5 MW electric-resistance heater (up to 530K output) and filtered (99.9% at 1-micron) just before entering the tunnel. Additional direct electrical heating of the facilities is used to help ensure thermal stability. The vacuum is supplied by a two-stage venturi air-ejector system capable of generating a vacuum of 4 torr. The maximum tunnel run time is 40 s, which is limited by the high mass-flow requirements for the ejector. The ACE tunnel can perform pitch and roll models during tunnel runs.
NAHL test capabilities with sponsors. (a) Hypervelocity Expansion Tunnel (HXT). (b) Mach 6 Quiet Tunnel (M6QT). (c) Actively Controlled Expansion (ACE) Tunnel. (d) Boundary Layer Turbulence (BOLT II) Hypersonic Flight Test.
Available flow conditions for NAHL facilities.
Instrumentation
The conventional instrumentation housed within the NAHL includes planar laser induced fluorescence (PLIF), molecular tagging velocimetry (MTV), vibrationally excited NO monitoring (VENOM), particle image velocimetry (PIV), hot-wire anemometry, pressure sensitive paint, temperature sensitive paints, conventional schlieren, focusing schlieren w/deflectometry, infrared thermography, high-speed (1 MHz) photography/focused schlieren, floating element skin friction sensors, and a Keyence LK-H022 laser profilometer with 0.02-micron resolution to quantify the surface finish. A key advantage of the NAL is the proximity to the Aerospace Laboratory for Lasers, Electromagnetics, and Optics (ALLEMO, Director R. Miles). This laboratory provides access to an extensive suite of advanced laser diagnostics including MHz pulse burst lasers, FLEET, two-photon PLIF, fs/ps hybrid CARS, filtered Rayleigh scattering, and Thomson scattering. The lab also contains many photonic devices and cameras, including a variety of single and multimode optical fibers, etalons, high-speed photodetectors and electro-optic devices including several visible and NIR acousto-optic modulators with RF amplifiers, electro-optic modulator, high-speed Shimadzu framing cameras (HPV-2 and HPV-X2), for 1+ MHz imaging, Photron SA-Z high speed camera for FLEET and high speed OES, LaVision High-Speed IRO intensifiers capable of operating at MHz rates with different photocathodes optimized for UV and NIR detection, Princeton Instruments Isoplane-160, and two Isoplane-320 imaging spectrometers with triple gratings for low and high resolution spectroscopy over UV-VIS-NIR, Light Machinery high-resolution NIR VIPA spectrometer, and PIMAX 1024i intensified cameras with dual gating capability.
Computations
The TAMU researchers have developed a suite of research codes to examine theoretical model performance; these codes include computational fluid dynamics codes, method of characteristics, and boundary layer solvers. The available government/commercial codes include DPLR CFD (NASA), US3D CFD (UMN, VirtusAero), Pointwise grid generation (Pointwise), and NEQAir (NASA) for non-equilibrium radiative transport and spectra. The team also utilizes the TAMU High Performance Research Computing and UT Texas Advanced Computing centers.
DNS simulation of Mach 6 turbulent boundary layer.